Don't use undefined as parent name in key warning

src/classic/element/ReactElementValidator.js

@@ -134,7 +134,8 @@ function validatePropertyKey(name, element, parentType) {
  */
 function warnAndMonitorForKeyUse(message, element, parentType) {
   var ownerName = getCurrentOwnerDisplayName();
-  var parentName = parentType.displayName || parentType.name;
+  var parentName = typeof parentType === 'string' ?
+    parentType : parentType.displayName || parentType.name;
 
   var useName = ownerName || parentName;
   var memoizer = ownerHasKeyUseWarning[message] || (
@@ -145,9 +146,10 @@ function warnAndMonitorForKeyUse(message, element, parentType) {
   }
   memoizer[useName] = true;
 
-  message += ownerName ?
-    ` Check the render method of ${ownerName}.` :
-    ` Check the React.render call using <${parentName}>.`;
+  message +=
+    ownerName ? ` Check the render method of ${ownerName}.` :
+    parentName ? ` Check the React.render call using <${parentName}>.` :
+    '';
 
   // Usually the current owner is the offender, but if it accepts children as a
   // property, it may be the creator of the child that's responsible for

src/classic/element/__tests__/ReactElementValidator-test.js

@@ -80,6 +80,46 @@ describe('ReactElementValidator', function() {
     );
   });
 
+  it('warns for keys for arrays with no owner or parent info', function() {
+    spyOn(console, 'warn');
+
+    var Anonymous = React.createClass({
+      displayName: undefined,
+      render: function() {
+        return <div />;
+      }
+    });
+
+    var divs = [
+      <div />,
+      <div />
+    ];
+    ReactTestUtils.renderIntoDocument(<Anonymous>{divs}</Anonymous>);
+
+    expect(console.warn.argsForCall.length).toBe(1);
+    expect(console.warn.argsForCall[0][0]).toBe(
+      'Warning: Each child in an array or iterator should have a unique ' +
+      '"key" prop. See http://fb.me/react-warning-keys for more information.'
+    );
+  });
+
+  it('warns for keys for arrays of elements with no owner info', function() {
+    spyOn(console, 'warn');
+
+    var divs = [
+      <div />,
+      <div />
+    ];
+    ReactTestUtils.renderIntoDocument(<div>{divs}</div>);
+
+    expect(console.warn.argsForCall.length).toBe(1);
+    expect(console.warn.argsForCall[0][0]).toBe(
+      'Warning: Each child in an array or iterator should have a unique ' +
+      '"key" prop. Check the React.render call using <div>. See ' +
+      'http://fb.me/react-warning-keys for more information.'
+    );
+  });
+
   it('warns for keys for iterables of elements in rest args', function() {
     spyOn(console, 'warn');
     var Component = React.createFactory(ComponentClass);